The present invention relates to a measurement device and a measurement method, and more particularly to a technique of analyzing an electron microscope image.
Semiconductor devices have been rapidly miniaturized and have reached the nanometer order in the early 2000s. Semiconductor devices are manufactured while various measurement devices typified by a critical dimension scanning electron microscope (CD-SEM) are used to measure the shape and dimensions of a circuit pattern in order to improve the yield of the products, and conform a difference between the circuit pattern and mask edge data. Especially, in a process (photolithography process) of transferring a photomask for the circuit pattern onto a wafer, it is important to measure the shape of the fine circuit pattern with high accuracy.
In the photolithography process, it is necessary to consider an optical proximity effect (optical diffraction effect) in order to form the circuit pattern of the nanometer order in accordance with the mask edge data of the circuit pattern. Regarding a simple mask shape 101 illustrated on the left side of FIG. 1A, a large difference between a shape 102 of a circuit pattern transferred on a wafer and a shape 103 of an edge of the mask shape 101 occurs due to the optical proximity effect, for example, as illustrated on the right side of FIG. 1A. In addition, a shape 104 of a corner is a round shape with recession tending to occur at an end of a line (EOL). A process (OPC: optical proximity correction) is introduced to change the photomask shape to a pattern shape 105 illustrated on the left side of FIG. 1B in order to obtain a desired pattern shape 106 illustrated on the right side of FIG. 1B. The OPC is a technique of improving the resolution of photolithography for correcting the shape of a transferred pattern by adjusting the width of a wiring and providing correction patterns for the EOL and the corner, for example.
Estimation of a parameter for a transfer model is required to apply the OPC to a photomask. According to a known document 1 (K. Lucas, “Optical Proximity Correction for Current and Future Nodes,” SPIE advanced lithography short course, SC990, 2010.) and a known document 2 (S. Shen, et al., “OPC model calibration based on circle-sampling theorem,” IEEE Solid-State and Integrated Circuit Technology, 2006.), a difference between an optical model and an actually exposed pattern occurs due to an effect of a resist, for example. Thus, the parameter for the transfer model is adjusted on the basis of a result of measurement of the length of a transfer pattern obtained by a CD-SEM. According to the known document 2, the series of processes are called OPC model calibration.
It is currently expected to achieve a method (hereinafter referred to as contour-based calibration) as one of new OPC model calibration methods. The method uses a CD value of a CD-SEM for a straight line portion of a circuit pattern to achieve two-dimensional positional coordinates of an SEM contour as calibration data for the other part of the circuit pattern. According to a known document 3 (P. Filitchkin, et al., “Contour quality assessment for OPC model calibration,” Proceedings of SPIE, Vol. 7272, pp. 72722Q1-7, 2009.) and a known document 4 (T. Shibahara, et al., “CD-gap-free Contour Extraction Technique for OPC Model Calibration,” Proceedings of SPIE, Vol. 7971, 2011.), in order to perform the contour-based calibration, it is necessary to measure an SEM contour that causes a short difference (hereinafter referred to as a CD-gap) between a conventional value and a CD measured length.
It is necessary to reduce the calibration time by sampling two-dimensional positional coordinate values of an SEM contour at appropriate intervals and reducing the amount of data since the calibration data in the OPC model calibration requires great time to analyze. The OPC model calibration with the data amount reduced, however, still has a problem with requiring several days to complete the process by a high-performance calculator.
If all SEM contour data is used for the OPC model calibration, the data amount to be calculated may be too large to be stored in a main storage device and to be processed depending on the performance of a calculator. It is necessary to reduce the SEM contour data amount for any of the problems to perform the contour-based calibration.